Apparently serebii.net received some leaked info on the long awaited Celebi Event. The event is set to happen from
February 21st to
March 6th at any local participating GameStop.
You can receive Celebi in Diamond, Pearl, Platinum, Heart Gold, and Soul Silver. However, there is a special in-game event when you receive it in Heart Gold and Soul Silver. When you do receive Celebi in HG/SS, take it to the shrine in Ilex Forest to trigger the event.
Then when Black and White comes out, you can transfer Celebi over to receive another gift. When you've sent Celebi over, go to the GameFreak Headquarters in Castelia City and receive a Zorua from one of them.
http://www.pokemongoldsilver.com/us/#/news/celebi/